Optical recording medium and its recording system

ABSTRACT

An optical recording medium and a recording system for the same are provided, which can dissipate heat produced by a laser beam during recording operations to thereby increase the erasing power margin of the laser beam which allows the playback jitter value to take on a certain value or less.  
     A recording system  1  includes an optical recording medium  10  and an optical recording apparatus  30.  The optical recording medium  10  has a reflective film  16,  a second dielectric layer  18,  a recording layer  20,  a heat sink layer  24,  and a light-transmitting layer  26,  which are formed on a support substrate  12.  The heat sink layer  24  is made of a material having a certain range of thermal conductivity, e.g., alumina. The optical recording apparatus  30  allows a laser beam of 450 nm or less in wavelength to be incident from the light-transmitting layer  26  via a lens system having an objective lens with a numerical aperture of 0.7 or more. The optical recording medium  10  dissipates heat produced by the laser beam through the heat sink layer  24  to thereby prevent an increase in temperature of the recording layer  20,  such that the relation between the recording power Pw of the laser beam and the erasing power Pe satisfies 0.7≦Pe/Pw≦1.0.

TECHNICAL FIELD

[0001] The present invention relates to an optical recording medium, andmore particularly to an optical recording medium which has a wide powermargin and to a recording system for the same.

BACKGROUND ART

[0002] Conventional optical recording media (discs) such as CDs (CompactDiscs) and DVDs (Digital Versatile Discs) are fabricated such that theirvarious characteristics (electrical and mechanical properties) complywith predetermined specifications in their as-fabricated (initial)conditions, and as a basic property, their playback jitter values areparticularly required to be equal to or less than a certain value.

[0003] One of the factors responsible for variations in the playbackjitter value is the ratio between the recording power Pw of a laser beamemployed during recording operations and the erasing power Pe of a laserbeam applied to erase data before the radiation with the laser beam forthe recording operations.

[0004] In general, an increase in the ratio Pe/Pw, i.e., an increase inPe would cause self-erasing to occur during a recording operation due toheat generated by a laser beam employed during an erasing operation,thereby leading to degradation in playback jitter value.

[0005] Therefore, such a recording strategy has to be employed whichmakes the erasing power Pe of a laser beam as low as possible to preventdegradation in playback jitter value even when the erasing power Pe isincreased due to manufacturing variations of the semiconductor laser orvariations of the control system.

[0006] Explaining this in more detail, the aforementioned recordingscheme employed to read data allows an optical recording medium to beradiated with a reproducing laser beam along the tracks to detect thereflected light, thereby reading information carried by recording marks.On the other hand, to record data, the optical recording medium isradiated with a recording laser beam along the tracks, thereby formingrecording marks having a predetermined length. For example, a DVD-RW ora type of the user data-rewritable optical recording medium employsrecording marks having lengths corresponding to 3 T to 11 T and 14 T(where T is one clock cycle), thereby recording data.

[0007] In general, when data is recorded on an optical recording medium,the optical recording medium is not radiated with a recording laser beamthat has the same pulse width as the duration corresponding to thelength of a recording mark to be formed but with a recording laser beamof a train of the number of pulses determined in accordance with thetype of the recording mark to be formed, thereby forming recording markshaving a predetermined length. For example, to record data on theaforementioned DVD-RW, pulses as many as n−1 or n−2 (where n indicatesthe type of recording marks and takes on any one value of 3 to 11 and14) are successively impinged thereon, thereby forming any one of therecording marks having lengths corresponding to 3 T to 11 T and 14 T.Accordingly, for n−2, to form a recording mark having a lengthcorresponding to 3 T, one pulse is used, while to form a recording markhaving a length corresponding to 11 T, nine pulses are used. On theother hand, for n−1, to form a recording mark having a lengthcorresponding to 3 T, two pulses are used, while to form a recordingmark having a length corresponding to 11 T, ten pulses are used.

[0008] In general, to overwrite an optical recording medium, on whichdata has been once recorded, with data different therefrom, the train ofrecording marks corresponding to the currently recorded data is directlyoverwritten with a train of recording marks corresponding to theoverwrite data.

[0009] However, in the case where the data that has been stored on anoptical recording medium for a long time is directly overwritten withnew data, the old recorded data may be insufficiently erased in somecases. In particular, when an optical recording medium has been exposedto a hot and humid environment after data had been recorded thereon, theold recorded data is less prone to being erased. Accordingly, the directoverwriting of the data that has been stored on an optical recordingmedium for a long time with new data would cause degradation in thejitter of the new overwrite data, thereby causing a problem of beingunable to reproduce the data with accuracy in some cases. Such a problembecomes noticeable in recording operations performed at a high settingof data transfer rate (e.g., 35 Mbps or more).

[0010] To thoroughly erase such old data, the erasing power can beeffectively increased. However, to form recording marks having a goodshape, it is necessary to appropriately set the ratio (Pe/Pw) of theerasing power to the recording power of a recording laser beam for eachtarget optical recording medium. If the ratio of the erasing power tothe recording power is out of an appropriate range, recording markscannot be formed in a proper shape, thus causing significant degradationin jitter. The proper range in which the ratio of the erasing power tothe recording power falls is generally referred to as a “power margin,”which is desired to be wider for recording operations with betterstability. Accordingly, to thoroughly erase old data, such an opticalrecording medium is demanded which can provide better jitter even at ahigher ratio of the erasing power to the recording power.

[0011] On the other hand, in recent years, there has been a great demandfor an optical recording medium operable at further improved datatransfer rates. However, since the laser for recording operations needsto be driven at increased speeds to increase the data transfer rate, alower ratio (Pe/Pw) of the erasing power to the recording power wouldcause improper pulse tracking. For this reason, there is a need for anoptical recording medium which can provide good jitter even when ahigher ratio (Pe/Pw) of the erasing power to the recording power needsto be set for recording operations at higher data transfer rates.

[0012] However, the aforementioned recording strategy requires acomplicated control of the semiconductor laser. In particular, inhigh-speed recording operations, there is a problem that when recordingpulses for driving the semiconductor laser are significantly reduced inpulse width, the actual waveform of the laser beam could not properlyfollow the recording pulses at a reduced Pe/Pw.

[0013] There is also a problem that the recording strategy employed forDVD-RWs or the like operates at power levels of three values, i.e., therecording power, the erasing power, and the bottom power, which make therecording strategy complicated.

[0014] The present invention was developed in view of the aforementionedconventional problems. It is therefore an object of the-invention toprovide a recording system for an optical recording medium which canprevent self-erasing to provide improved playback jitter values andwhich can employ a recording strategy at power levels of substantiallytwo values.

[0015] It is another object of the present invention to provide anoptical recording medium having an increased power margin.

[0016] It is still another object of the present invention to provide anoptical recording medium which can provide good jitter even whenrecording marks are formed with a recording laser beam at a high ratioof the erasing power to the recording power.

DISCLOSURE OF THE INVENTION

[0017] That is, the following inventions achieve the aforementionedobjects.

[0018] The objects of the present invention are also achieved by (1) anoptical recording medium which has at least a recording layer andrecords information in the form of recording marks being created in therecording layer with a recording laser beam. The optical recordingmedium is characterized in that jitter of recording marks is 13% orless, the recording marks being formed at a Pe/Pw setting of 1.0, wherePw is a recording power of the recording laser beam and Pe is an erasingpower.

[0019] According to the present invention, because of a wide margin ofthe ratio of the erasing power to the recording power, data recordingcan be performed with stability with reduced jitter in directoverwriting of old data with new data even when the ratio of the erasingpower to the recording power is increased to thoroughly erase the olddata.

[0020] (2) An optical recording medium characterized in that the jitterof recording marks is 11% or less, the recording marks being formed at aPe/Pw setting of 1.0.

[0021] According to the invention set forth in (2), because of a widermargin of the ratio of the erasing power to the recording power, datarecording can be performed with better stability with further reducedjitter even at an increased ratio of the erasing power to the recordingpower.

[0022] (3) An optical recording medium characterized in that the jitterof recording marks is 10% or less, the recording marks being formed at aPe/Pw setting of 0.7.

[0023] According to the invention set forth in (3), because of a muchwider margin of the ratio of the erasing power to the recording power,data recording can be performed with much better stability with muchmore reduced jitter even at an increased ratio of the erasing power tothe recording power.

[0024] (4) An optical recording medium characterized in that the jitterof recording marks is 9% or less, the recording marks being formed at aPe/Pw setting of 0.7.

[0025] According to the invention set forth in (4), because of anextremely wider margin of the ratio of the erasing power to therecording power, data recording can be performed with far betterstability with significantly reduced jitter even at an increased ratioof the erasing power to the recording power.

[0026] (5) An optical recording medium further including alight-transmitting layer provided on the side of incidence of therecording laser beam, and a dielectric layer and a heat ink layerprovided between the recording layer and the light-transmitting layer.

[0027] (6) An optical recording medium characterized in that the heatsink layer has a thickness of 10 to 200 nm.

[0028] According to the invention set forth in (6), it is possible toobtain a wide power margin with stability without excessively reducingthe throughput of manufacturing processes.

[0029] (7) An optical recording medium characterized in that the heatsink layer has a thickness of 30 to 100 nm.

[0030] According to the invention set forth in (7), it is possible toobtain a wide power margin with better stability without excessivelyreducing the throughput of manufacturing processes.

[0031] (8) A recording system for an optical recording medium, thesystem including an optical recording medium provided with at least alight-transmitting layer covered with a recording layer formed on asupport substrate, and a radiation optical system for recording,reproducing, and erasing information on/from the recording layer byradiating the optical recording medium from the light-transmitting layerside with a laser beam at a recording power Pw and an erasing power Pe.The radiation optical system is designed to radiate the recording layerwith a laser beam of wavelength 450 nm or less through a lens systemhaving an objective lens of numerical aperture 0.7 or more. The opticalrecording medium is designed to be able to record or erase informationon the recording layer when the relation between the recording power Pwof the laser beam and the erasing power Pe satisfies 0.7≦Pe/Pw≦1.0.

[0032] (9) The recording system for an optical recording mediumaccording to (8), wherein the radiation optical system is designed toradiate the recording layer to record information thereon with a laserbeam of wavelength 450 nm or less through a lens system having anobjective lens of numerical aperture 0.7 or more, and the opticalrecording medium is designed to provide a playback jitter value of 10%or less for the information recorded.

[0033] As used herein, the term “jitter” refers to the clock jitterhaving a value that is determined as in σ/Tw (%), where a is the signalfluctuation obtained by measuring a playback signal with a time intervalanalyzer and Tw is the detection window width.

[0034] (10) The recording system for an optical recording mediumaccording to (8) or (9), wherein the radiation optical system isdesigned such that the laser beam has a wavelength of 380 nm or more.

[0035] (11) The recording system for an optical recording mediumaccording to (8) or (9), wherein the radiation optical system isdesigned such that the laser beam has a wavelength of 405 nm, and thelens system is designed to have an objective lens of numerical aperture0.85.

[0036] (12) The recording system for an optical recording mediumaccording to any of (8) to (11), wherein the recording layer isprovided, on its light-transmitting layer side, with a heat sink layer.

[0037] (13) The recording system for an optical recording mediumaccording to (12), wherein the heat sink layer has a thickness of 10 nmor more and 200 nm or less, preferably, has a thickness of 30 nm or moreand 100 nm or less.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038]FIG. 1 is a block diagram illustrating a recording systemaccording to an embodiment of the present invention;

[0039]FIG. 2 is a schematic cross-sectional view illustrating the layerstructure of an optical recording medium employed for the recordingsystem;

[0040]FIG. 3 is a flowchart showing a method of fabricating an opticalrecording medium 10;

[0041]FIG. 4 is a diagram showing the relation between the pulsestrategy and the emission waveform of a laser beam for recordingoperations on an optical recording medium in a recording systemaccording to the embodiment;

[0042]FIG. 5 is a diagram showing the relation between the pulsestrategy and the emission waveform of a laser beam for an opticalrecording medium having no heat sink layer according to the presentinvention;

[0043]FIG. 6 is an exemplary view illustrating the recording strategyfor forming a recording mark having a length corresponding to 2 T;

[0044]FIG. 7 is a diagram showing the relation between the playbackjitter value and the ratio Pe/Pw of the erasing power Pe to therecording power Pw of a laser beam according to Example 1 of the presentinvention and Comparative example 1;

[0045]FIG. 8 is a diagram showing the relation between the playbackjitter value and the Pe/Pw with the recording power of a laser beamvaried according to Example 2 of the present invention;

[0046]FIG. 9 is a diagram showing the relation between the playbackjitter value and the ratio Pe/Pw of the erasing power Pe to therecording power Pw of a laser beam according to Example 3 of the presentinvention and Comparative example 2;

[0047]FIG. 10 is a diagram showing the relation between the playbackjitter value and the Pe/Pw with the recording power of a laser beamvaried according to Example 4 of the present invention; and

[0048]FIG. 11 is a diagram illustrating the relation between theplayback jitter value and the ratio Pe/Pw of the erasing power Pe to therecording power Pw of a laser beam according to Example 5 of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0049] Now, the present invention will be explained below in more detailwith reference to the drawings in accordance with the embodiment.

[0050] As shown in an enlarged schematic view in FIG. 2, an opticalrecording medium 10 used with a recording system 1, shown in FIG. 1,according to this embodiment is provided with at least a reflective film16, a second dielectric layer 18, a recording layer 20, a firstdielectric layer 22, and a light-transmitting layer 26, which are formedin that order on top of (“under” in FIG. 2) a support substrate 12 madeof polycarbonate, and with a heat sink layer 24 between the firstdielectric layer 22 and the light-transmitting layer 26, as required.

[0051] In this embodiment, the support substrate 12 is formed ofpolycarbonate resin by injection molding in a thickness of about 1.1 mm.On top thereof, the reflective film 16, the second dielectric layer 18,the recording layer 20, and the first dielectric layer 22, as well asthe heat sink layer 24 (as required) are formed in that order bysputtering, with the light-transmitting layer 26 being formed ofacrylic-based resin by spin coating in a thickness of about 100 μm.There is provided a hole 28 at the center portion of the opticalrecording medium 10. The optical recording medium 10 having such astructure is radiated with a recording laser beam from thelight-transmitting layer 26 side to thereby record data, while beingradiated with a reproducing laser beam from the light-transmitting layer26 side to thereby reproduce data.

[0052] Accordingly, the light-transmitting layer 26 is formed to beconsiderably thicker in thickness than a resin layer corresponding tothe position of the light-transmitting layer 26 in the optical recordingmedium 10 or a protective layer (about 5 to 10 μm in thickness) on thereflective layer in conventional CDs or DVDs or the like.

[0053] Only by way of example, the support substrate 12 is formed ofpolycarbonate as mentioned above. Although the reflective film 16 can beformed of any type of metal materials without limitation as long as itsatisfies the required reflectivity, it is formed of an alloy composedmainly of Ag in this embodiment. Although the first and seconddielectric layers 22, 18 can also be formed of any type of materials,the second dielectric layer 13 is formed of Al₂O₃ and the firstdielectric layer 15 is formed of ZnS—SiO₂ in this embodiment in thisembodiment. The recording layer 20 is formed of AgInSbTeGe-basedmaterial having a phase change recording-layer composition. Thelight-transmitting layer 26 is formed of an UV curable resin.

[0054] The heat sink layer 24 is formed of a material having a thermalconductivity k, where k>1 W·m⁻¹ K⁻¹, e.g., alumina (Al₂O₃).

[0055] The heat sink layer 24 is a layer for efficiently radiating heatgiven to the recording layer 20, serving to provide an additional powermargin to the optical recording medium 10. Accordingly, the thermalconductivity of the heat sink layer 24 is required to be higher at leastthan that of the first dielectric layer 22.

[0056] On the other hand, the support substrate 12 has a thickness ofabout 1.1 mm, the reflective film 16 has a thickness of 10 to 300 nm,the second dielectric layer 18 has a thickness of 2 to 50 nm, therecording layer 20 has a thickness of 5 to 30 nm, the first dielectriclayer 22 has a thickness of 10 to 300 nm, and the light-transmittinglayer 26 has a thickness of 10 to 300 μm, preferably, 50 to 150 μm.However, the present invention is not limited thereto.

[0057] If the thickness of the heat sink layer 24 is below 10 nm, thethickness is controlled with difficulty, while a slight variation inthickness would cause a significant variation in the power margin. Onthe other hand, at a thickness of 30 nm or more would make it possibleto obtain a noticeable effect of increasing the power margin. Incontrast, an excessively greater thickness of the heat sink layer 24would require elongated time for deposition, thereby causing not only adecrease in throughput but also a danger of thermal damage to asubstrate 11. In consideration of the foregoing, the heat sink layer 24is set at 10 to 200 nm in thickness, preferably, to 30 to 100 nm.

[0058] The recording layer 20 (AgInSbTeGe) of the optical recordingmedium 10 is made of a phase change film having different values ofreflectivity between in the crystalline state and in the amorphousstate, which is utilized for recording data. More specifically, therecording layer 20 of a non-recorded area is in the crystalline statewith 20% reflectivity, for example. To record any data onto such anon-recorded area, a predetermined portion in the recording layer 20 isheated to a temperature higher than the melting point in accordance withthe data to be recorded and then quickly cooled down into an amorphousstate. The portion in the amorphous state has, e.g., 7% reflectivity,thus allowing the predetermined data to be recorded. To overwrite dataonce recorded, the portion of the recording layer 14 on which the datato be overwritten is recorded is heated to a temperature equal to orhigher than the crystallization point or the melting point in accordancewith data to be recorded, and thus changed into the crystalline state oran amorphous state.

[0059] In this case, the relation between the power Pw (recording power)of a recording laser beam with which the recording layer 20 is radiatedto melt, the power Pb (ground power) of a recording laser beam withwhich the recording layer 20 is radiated to cool down, and the power Pe(erasing power) of a recording laser beam with which the recording layer20 is radiated to crystallize is expressed by Pw>Pe>Pb.

[0060] The optical recording medium 10 according to this embodimentpreferably stores “recording condition setting information,” though thepresent invention is not limited thereto The recording condition settinginformation refers to various conditions necessary to record/reproducedata on/from the optical recording medium 10, e.g., information used foridentifying the power of a recording laser beam or a recording strategy.The recording condition setting information includes not only thosepieces specifically indicative of each condition necessary torecord/reproduce data but also those pieces for identifying arecording/reproduction condition by specifying any of the variousconditions pre-stored in an information recording apparatus.

[0061] On the other hand, the “recording strategy” refers to a method ofradiation with a recording laser beam to form recording marks, i.e., thesettings such as the number of recording laser beam pulses, the pulsewidth of each pulse, the pulse interval, and the power of recordinglaser beams (Pw, Pe, and Pb). The “recording strategy” is determined inaccordance with the recording condition setting information stored inthe optical recording medium 10.

[0062] To record data on the optical recording medium 10 according tothis embodiment, it is necessary to set the ratio (Pe/Pw) of the erasingpower Pe to the recording power Pw of a recording laser beam within anappropriate range. If the ratio (Pe/Pw) of the erasing power Pe to therecording power Pw is out of the appropriate range, recording markscannot be formed in a proper shape, thus causing significant degradationin jitter. Suppose that the jitter is defined as jitter (1.0) when theratio (Pe/Pw) of the erasing power Pe to the recording power Pw is 1.0.In this case, the optical recording medium 10 according to thisembodiment satisfies the condition given by

Jitter (1.0)<13%   (1).

[0063] Thus, the optical recording medium 10 according to thisembodiment allows old data to be overwritten directly with new data,effectively preventing degradation in jitter even when the ratio of theerasing power to the recording power is increased to thoroughly erasethe old data. Additionally, the optical recording medium 10 according tothis embodiment preferably satisfies the condition given by

Jitter (1.0)<11%   (2).

[0064] With such a condition satisfied, degradation in jitter is moreeffectively prevented in overwriting old data directly with new dataeven when the ratio of the erasing power to the recording power isincreased to thoroughly erase the old data.

[0065] Furthermore, suppose that the jitter is defined as jitter (0.7)when the ratio (Pe/Pw) of the erasing power Pe to the recording power Pwis 0.7. In this case, the optical recording medium 10 according to thisembodiment more preferably satisfies the condition given by

Jitter (0.7)<10% ,  (3).

[0066] With such a condition satisfied, degradation in jitter isprevented much more effectively in overwriting old data directly withnew data even when the ratio of the erasing power to the recording poweris increased to thoroughly erase the old data. Additionally, the opticalrecording medium 10 according to this embodiment more preferablysatisfies the condition given by

Jitter (0.7)<9%   (4).

[0067] With such a condition satisfied, degradation in jitter isprevented very effectively in directly overwriting old data with newdata even when the ratio of the erasing power to the recording power isincreased to thoroughly erase the old data.

[0068] Now, a method for fabricating the optical recording medium 10according to this embodiment will be described below.

[0069]FIG. 3 is a flowchart showing the method for fabricating theoptical recording medium 10 according to this embodiment. As describedabove, the light-transmitting layer 26 of the optical recording medium10 is as very thin as 10 to 300 μm in thickness, thus being deposited inthe reverse order to that for the typical conventional DVD-RWs.

[0070] First, a stamper is used to injection mold a substrate 11 havinga thickness of about 1.1 mm, with a pre-groove of groove width about0.151 μm, track pitch about 0.32 μm, and groove depth about 20 nm (stepS1).

[0071] Then, the support substrate 12 is transported into a firstchamber (not shown) of a sputtering apparatus. The sputtering apparatusis provided in the first chamber with an alloy composed mainly of silveras a target. Then, the first chamber is pumped into a vacuum of about1×10⁻⁴ Pa. Subsequently, an argon gas is introduced into the firstchamber to set the gas pressure at 0.1 to 1.0 Pa. Thereafter, a DC or RFvoltage is applied to the target for sputtering. In this manner, on topof the support substrate 12, formed is a reflective film 16 of 10 to 300nm in thickness (step S2).

[0072] Then, the support substrate 12 having the reflective film 16formed thereon is transported from the first chamber to a second chamber(not shown). In the second chamber of the sputtering apparatus, providedis Al₂O₃ as a target. Then, the second chamber is pumped into a vacuumof about 1×10⁻⁴ Pa. Subsequently, an argon gas is introduced into thesecond chamber to set the gas pressure at 0.1 to 1.0 Pa for sputtering.In this manner, on top of the reflective film 16, formed is a seconddielectric layer 18 having a thickness of 2 to 50 nm (step S3).

[0073] Then, the support substrate 12 having the reflective film 16 andthe second dielectric layer 18 formed thereon is transported from thesecond chamber to a third chamber (not shown). In the third chamber ofthe sputtering apparatus, provided is a target mixture of Ag, In, Sb,Te, and Ge. Then, the third chamber is pumped into a vacuum of about1×10⁻⁴ Pa. Subsequently, an argon gas is introduced into the thirdchamber to set the gas pressure at 0.1 to 1.0 Pa for sputtering. In thismanner, on top of the second dielectric layer 18, formed is a recordinglayer 20 having a thickness of 5 to 30 nm (step S4).

[0074] Then, the support substrate 12 having the reflective film 16 tothe recording layer 20 formed thereon is transported from the thirdchamber to a fourth chamber (not shown). In the fourth chamber of thesputtering apparatus, provided is a target mixture of ZnS and SiO₂.Then, the fourth chamber is pumped into a vacuum of about 1×10⁻⁴ Pa.Subsequently, an argon gas is introduced into the fourth chamber to setthe gas pressure at 0.1 to 1.0 Pa for sputtering. In this manner, on topof the recording layer 20, formed is a first dielectric layer 22 havinga thickness of 10 to 300 nm (step S5).

[0075] Then, the support substrate 12 having the reflective film 16 tothe first dielectric layer 22 formed thereon is transported from thefourth chamber to a fifth chamber (not shown). In the fifth chamber ofthe sputtering apparatus, provided is a target of Al₂O₃. Then, the fifthchamber is pumped into a vacuum of about 1×10⁻⁴ Pa. Subsequently, anargon gas is introduced into the fifth chamber to set the gas pressureat 0.1 to 1.0 Pa for sputtering. In this manner, on top of the firstdielectric layer 22, formed is a heat sink layer 24 having a thicknessof 10 to 200 nm, preferably, 30 to 100 nm (step S6). The sputtering ofthe heat sink layer 24 may also be carried out in the second chamber.

[0076] In this manner, the reflective film 16, the second dielectriclayer 18, the recording layer 20, the first dielectric layer 15, and theheat sink layer 24 are completely formed on the support substrate 12.Then, the support substrate 12 having each of these layers formedthereon is taken out of the fifth chamber of the sputtering apparatusand then coated on the surface of the heat sink layer 24 with an UVcurable resin such as by spin coating, by roll coating, or by screenprinting. Then, the resulting substrate 12 is radiated with anultraviolet radiation to thereby form a light-transmitting layer 17having a thickness of about 10 to 300 μm (step S7). In the foregoing,the optical recording medium 10 according to this embodiment iscompleted. To form the light-transmitting layer 26, a pre-molded resinsheet material such as of polycarbonate or polyolefin may also beadhered to the surface of the heat sink layer 24.

[0077] Now, an optical recording/reproducing apparatus 30 for recordingdata onto the optical recording medium 10 in the optical recordingsystem 1 will be described with reference to FIG. 1.

[0078]FIG. 1 is a schematic view illustrating the main portion of apreferred information recording apparatus for recording data on theoptical recording medium 10.

[0079] As shown in FIG. 1, the information recording/reproducingapparatus 30 illustrated includes a spindle motor 2 for rotating theoptical recording medium 10, a head 3 for radiating the opticalrecording medium 10 with a recording laser beam, a controller 4 forcontrolling the operations of the spindle motor 2 and the head 3, alaser drive circuit 5 for supplying a laser drive signal to the head 3,and a lens drive circuit 6 for supplying a lens drive signal to the head3.

[0080] Furthermore, as shown in FIG. 1, the controller 4 includes afocus servo follower circuit 7, a tracking servo follower circuit 8, anda laser control circuit 9. Activating the focus servo follower circuit 7would allow the recording surface of the optical recording medium 10being rotated to be focused, while activating the tracking servofollower circuit 8 would allow the spot of a laser beam to automaticallyfollow an eccentric signal track of the optical recording medium 10. Thefocus servo follower circuit 7 and the tracking servo follower circuit 8are each provided with an automatic gain control function forautomatically adjusting focus gain and an automatic gain controlfunction for automatically adjusting tracking gain, respectively. Thelaser control circuit 9 generates a laser drive signal to be supplied bythe laser drive circuit 5, while generating an appropriate laser drivesignal in accordance with recording condition setting information storedin-the optical recording medium 10, if any.

[0081] These focus servo follower circuit 7, the tracking servo followercircuit 8, and the laser control circuit 9 do not always need to be acircuit incorporated into the controller 4 but may also be a componentseparated from the controller 4. Furthermore, these circuits need not tobe always in the form of a physical circuit but may also be in the formof software to be executed in the controller 4.

[0082] Although not limited to the following particular arrangement, theinformation recording apparatus suitable for recording data onto theoptical recording medium 10 employs preferably a recording laser beam ofwavelength 450 nm or less, preferably 380 to 450 nm, more preferably 405nm, and an objective lens (not shown) or part of the head 3 for focusinga recording laser beam, having an NA (numerical aperture) of 0.7 ormore. In recording data onto the optical recording medium 10 using suchan information recording apparatus, a distance (working distance) to beset between the objective lens and the surface of the optical recordingmedium 10 is very small (e.g., about 80 to 150 μm), thereby making itpossible to realize a beam spot of a significantly reduced diameter ascompared with the conventional one. This makes it possible to realize anextremely high data transfer rate (e.g., 35 Mbps or greater) inrecording data onto the optical recording medium 10 using such aninformation recording apparatus.

[0083] Additionally, as described above, in recording data onto theoptical recording medium 10 according to this embodiment using such aninformation recording apparatus 30, a recording strategy determined inaccordance with recording condition setting information stored on theoptical recording medium 10, if any, is used to determine the ratio ofthe erasing power Pe to the recording power Pw of the recording laserbeam.

[0084] More specifically, the recording layer 20 is radiated with theaforementioned laser beam from the light-transmitting layer 26 side viathe objective lens at the recording power Pw or the erasing power Pe,thereby recording or erasing information on the recording layer 20. Theoptical recording medium 10 is also designed to provide a jitter valuebelow 10% at the time of reproducing the information that has beenrecorded by being radiated with a laser beam under the condition of0.7≦Pe/Pw≦1.0.

[0085] The heat sink layer 24 has a thickness of 10 nm or more because athickness of less than 10 nm would cause the power margin of the laserbeam to be significantly varied due to a slight variation in thickness.Accordingly, the thickness is preferably determined to be 30 nm or more.

[0086] Furthermore, the aforementioned thickness is 200 nm or lessbecause a thickness greater than 200 nm would require an excessive timefor its deposition during manufacturing, simultaneously causingincreased thermal damage to the support substrate 12. Accordingly, thethickness is determined to be 200 nm or less, more preferably 100 nm orless.

[0087] As described above, the optical recording medium 10 according tothis embodiment makes the playback jitter value below 10% even when theerasing power Pe of an erasing laser beam is within the range of0.7≦Pe/Pw≦1.0 relative to the recording power Pw. For example, as shownin FIG. 3, the emission waveform of a laser beam actually emitted from alaser 36 (see FIG. 1) has a very good trackability to the recordingpulse signal for driving the laser 36. FIG. 4(A) shows a recordingtransfer rate of 35 Mbps, while FIG. 4(B) shows a rate of 100 Mbps.

[0088] In contrast to this, suppose that Pe/Pw is about 0.5. In thiscase, as shown in FIGS. 5(A) and 5(B), the emission waveform has a lowertrackability to the recording pulse signal. Particularly, in the case ofa recording transfer rate of 100 Mbps as shown in FIG. 5(B), therecording pulse signal having a narrow pulse width will fall before theemission waveform completely rises.

[0089] That is, the heat sink layer 24 is provided to accelerate theradiation of heat from the recording layer 20 and prevent the heat frombeing accumulated therein. Thus, this will not allow the heat to causeself-erasing during recording operations even when the erasing power Peof a laser beam for erasing operations is made higher than theconventional level relative to the recording power Pw. Accordingly, itis possible to prevent degradation in playback jitter value.

[0090] To record information onto the recording layer 20, the recordingpower Pw of a laser beam multiplied by the pulse width of a recordingpulse equal to the amount of input heat has to be in a predeterminedrange.

[0091] The optical recording medium 10 according to this embodiment isprovided with the heat sink layer 24 and thereby allows heat to readilyescape from the recording layer 20, thus making it possible to set thepulse width in a wide range at a constant recording power Pw. Incontrast to this, without the heat sink layer 24, the amount of targetinput heat can be reached in a short time, thus providing a lower degreeof flexibility in the setting range of pulse width.

[0092] In the aforementioned embodiment, the heat sink layer 24 is madeof alumina. The present invention is not limited thereto but may alsoemploy a material having a thermal conductivity within theaforementioned range and formable in the shape of film for covering therecording layer 20 therewith, e.g., aluminum nitride or the like.

[0093] Additionally, in the aforementioned embodiment, thelight-transmitting layer 26 is made of an acryl-based resin; however,any type of material can also be selected from the group of an energybeam curable resin that is hardened by an energy beam such as anultraviolet ray or a thermally curable resin that is hardened by heat,thus making the acryl-based resin, the epoxy-based resin, theurethane-based resin or the like applicable. It is also possible toemploy a pre-formed resin film such as of polycarbonate or polyolefinfor adhesion or the like.

[0094] Furthermore, the support substrate 12 may also be made ofpolyolefin or the like other than the polycarbonate as employed in theembodiment.

[0095] The aforementioned information recording apparatus 30 can alsoemploy a (1, 7) RLL modulation scheme, though the present invention isnot limited thereto. However, the information recording apparatus forrecording data onto the optical recording medium 10 does not always needto employ such a modulation scheme to record data but may also employother modulation schemes for recording data.

[0096] Now, an exemplary recording strategy will be described belowwhich employs the (1, 7) RLL modulation scheme.

[0097]FIG. 6 is a view illustrating an exemplary recording strategy forforming a recording mark of a length corresponding to 2 T.

[0098] As shown in FIG. 6, to form a recording mark of a lengthcorresponding to 2 T, the number of recording laser beam pulses is setat “1.” In the foregoing, the number of recording laser beam pulses isdefined by the number of times of raising the power of the recordinglaser beam up to Pw. In more detail, suppose that the timing at whichthe recording laser beam is positioned at the start point of a recordingmark is time ts, and the timing at which the recording laser beam ispositioned at the end point of the recording mark is time te. In thiscase, the power of the recording laser beam is raised once up to Pw andthen to power Pb during the period from time ts to time te. The power ofthe recording laser beam is set at Pe before time ts, allowing therecording laser beam to start rising at time ts. On the other hand, thepower of the recording laser beam at time te is set at Pe or Pb.

[0099] During the duration of Tpulse, the recording layer 20 of theoptical recording medium 10 is subjected to a high energy to have atemperature higher than the melting point, whereas during the durationof Tcl, the recording layer 20 of the optical recording medium 10 isquickly cooled down. This allows the recording mark of a lengthcorresponding to 2 T to be formed in the recording layer 20 of theoptical recording medium 10.

[0100] To form a recording mark of another length, as in the case offorming the recording mark of the length corresponding to 2 T, the powerof the recording laser beam is set at Pw, Pe, or Pb, thus formingrecording marks having a desired length each by a predetermined numberof pulses.

[0101] The optical recording medium 10 according to this embodimentprovides a wide power margin as described above. It is thereforepossible to reduce jitter in directly overwriting old data with new data

[0102] even when the ratio of the erasing power to the recording poweris increased to thoroughly erase the old data. Accordingly, even withrecording operations performed at a high setting of data transfer rate(e.g., 35 Mbps or more), the old data can be thoroughly erased.

[0103] Now, examples of the present invention will be explained indetail below.

EXAMPLE 1

[0104] An optical recording medium was prepared in accordance with thefollowing procedures.

[0105] A disc-shaped support substrate was employed which was made of apolycarbonate resin like in the aforementioned embodiment and which hada surface having grooves formed thereon (the depth of the grooves wasλ/18 in terms of an optical path length at a wavelength λ=405 nm with arecord track pitch of 0.32 μm). On top of this surface, a reflectivefilm composed mainly of silver was formed by sputtering in a thicknessof 100 nm.

[0106] Then, on the surface of the reflective film, formed was a seconddielectric layer of Al₂O₃ by sputtering in a thickness of 20 nm.

[0107] Additionally, a recording layer was formed by sputtering in athickness of 12 nm on the second dielectric layer using an alloy targetof a phase change material. This recording layer was chosen to have acomposition of AgInSbTeGe.

[0108] Furthermore, on the surface of the recording layer, a dielectriclayer was formed by sputtering in a thickness of 30 nm using a ZnS(80mol %)-SiO₂(20 mol %) target.

[0109] On the surface of this dielectric layer, as with theaforementioned second dielectric layer, a heat sink layer of Al₂O₃ wasformed by sputtering in a thickness of 60 nm.

[0110] Then, the surface of the heat sink layer was coated by spincoating with an UV curable resin, and then radiated with an ultravioletradiation to thereby obtain a light-transmitting layer of 10 μm inthickness.

Comparative Example 1

[0111] Furthermore, an optical recording medium was prepared asComparative example 1 which had the heat sink layer removed from theaforementioned example 1.

[0112] As with the aforementioned embodiment, recording operations wereperformed with these examples under the conditions of a wavelength λ=405nm and a numerical aperture of the objective lens NA=0.85, at therecording power Pw of a laser beam fixed to 6.0 mW, with the erasingpower Pe of a laser beam being varied so that the Pe/Pw was 0.25 to1.00. Thereafter, the playback jitter value was measured as shown inFIG. 7.

[0113] As can be seen from FIG. 7, the upper limit value of the Pe/Pwproviding a playback jitter value of 10% or less is 0.67 in thecomparative example, whereas being 0.87 in the case of the example ofthe present invention. Furthermore, the upper limit value of the Pe/Pwproviding a jitter value of 13% or less is about 0.75 in the comparativeexample, whereas being above 1.0 in the example of the presentinvention.

[0114] This can be listed as shown in Table 1 below. TABLE 1 Playbackjitter value (%) Pe/Pw Example Comparative example 0.5 7.5 8.0 0.6 7.58.3 0.7 8.3 11.0 0.8 8.5 >14 0.9 9.2 — 1.0 11.1 —

EXAMPLE 2

[0115] In Example 2, with the heat sink layer changed to be 30 nm inthickness, recording operations were performed on the optical recordingmedium configured in the same manner as in Example 1 at each recordingpower Pw of a laser beam selected from 3.8 mW, 4.2 mW, and 6.0 mW withthe erasing power Pe being varied relative to these recording powers Pwsuch that Pe/Pw was in the range of 0.3 to 1.1. Then, the playbackjitter values were measured as shown in FIG. 8.

[0116] From FIG. 8, it can be seen that even when the recording power ofa laser beam is varied, the playback jitter value can be made 10% orless if the Pe/Pw is within the range of the embodiment.

EXAMPLE 3

[0117] Example 3 employs the same optical recording medium as that ofExample 2. The optical recording medium of Example 3 was provided withthe first dielectric layer of 45 nm in thickness without the heat sinklayer to prepare Comparative example 2. Recording operations wereperformed on the comparative example 2 and Example 3 with the Pe/Pwbeing varied in the range of 0.3 to 1.0. Then, the playback jittervalues were-measured as shown in FIG. 9.

[0118] As seen from FIG. 9, the comparative example having no heat sinklayer provides a jitter value of above 10% at the point of Pe/Pwexceeding 0.60, while providing a jitter value of above 13% at 0.80.

[0119] In contrast to this, the optical recording medium of Example 3never exceeds a playback jitter value of 10% even at a Pe/Pw of 1.0.

EXAMPLE 4

[0120] The aforementioned method was employed to fabricate an opticalrecording medium 10-1 having the structure shown in FIG. 2, with thesupport substrate 12 having a thickness of 1.1 mm, the reflective film16 having a thickness of 100 nm, the second dielectric layer 18 having athickness of 20 nm, the recording layer 20 having a thickness of 12 nm,the first dielectric layer 22 having a thickness of 30 nm, the heat sinklayer 24 having a thickness of 30 nm, and the light-transmitting layer26 having a thickness of 100 μm.

[0121] With the optical recording medium 10-1, under the conditionsshown in Table 2, the recording power Pw was set at 3.8 mW and a signalmixture of recording marks having lengths corresponding to 2 T to 8 Twas formed using various erasing powers Pe. Then, the recording power Pwwas set at 4.2 mW and a signal mixture of recording marks having lengthscorresponding to 2 T to 8 T was formed using various erasing powers Pe.Furthermore, the recording power Pw was set at 6.0 mW and a signalmixture of recording marks having lengths corresponding to 2 T to 8 Twas formed using various erasing powers Pe. The ground power Pb was setat 0.1 mW in all the cases. The (1, 7) RLL modulation scheme wasemployed for recording operations to record data only on one track.TABLE 2 Clock frequency 66 MHz Clock cycle (1T) 15.15 nsec Linear speed5.3 m/sec Modulation scheme (1,7) RLL Format efficiency 80% Datatransfer rate 35 Mbps (efficiency considered) Channel bit length 0.12μm/bit Numerical aperture (NA) 0.85 Laser wavelength 405 nm

[0122] Then, the clock jitter of the signal mixture created on theoptical recording medium 10-1 was measured. In the measurements, a timeinterval analyzer was used to determine the “fluctuation a” of theplayback signal to calculate σ/Tw (where Tw is one clock cycle). 15 Theresults of the measurements are shown in FIG. 10.

[0123] As shown in FIG. 10, at any setting of the recording power Pw to3.8 mW, 4.2 mW, or 6.0 mW, the optical recording medium 10-1 providesthe jitter (1.0) as shown below when the ratio (Pe/Pw) of the erasingpower Pe to the recording power Pw is 1.0. That is,

Jitter (1.0)<11%.

[0124] Furthermore, at any setting of the recording power Pw to 3.8 mW,4.2 mW, or 6.0 mW, the optical recording medium 10-1 provides the jitter(0.7) as shown below when the ratio (Pe/Pw) of the erasing power Pe tothe recording power Pw is 0.7. That is,

Jitter (0.7)<9%.

[0125] As described above, it was confirmed that irrespective of thesetting of the recording power Pw, the optical recording medium 10-1provides reduced jitter and a very wide power margin even at a highsetting of the ratio (Pe/Pw) of the erasing power Pe to the recordingpower Pw.

EXAMPLE 5

[0126] The aforementioned method was employed to fabricate an opticalrecording medium 10-2 having the structure shown in FIG. 2, with thesupport substrate 12 of 1.1 mm in thickness, the reflective film 16 of100 nm in thickness, the second dielectric layer 18 of 20 nm inthickness, the recording layer 20 of 12 nm in thickness, the firstdielectric layer 22 of 45 nm in thickness, and the heat sink layer 24 of0 nm in thickness. The optical recording medium 10-2 is different fromthe aforementioned optical recording medium 10-1 in that the firstdielectric layer 22 was changed to have a thickness of 45 nm and theheat sink layer 24 was changed to be 0 nm (no heat sink layer wasprovided).

[0127] With the optical recording medium 10-2, under the conditionsshown in Table 2, the recording power Pw was set at 5.8 mW and a signalmixture of recording marks having lengths corresponding to 2 T to 8 Twas formed using various erasing powers Pe. The (1, 7) RLL modulationscheme was employed for recording operations to record data only on onetrack.

[0128] Then, the clock jitter of the signal mixture created on theoptical recording medium 10-2 was measured.

[0129] The results of the measurements are shown in FIG. 11. FIG. 11also shows the results of measurements made when the recording power Pwwas set at 6.OmW with the optical recording medium 10-1.

[0130] As shown in FIG. 11, it is seen that the optical recording medium10-2 satisfies

Jitter (1.0)<13%, and

Jitter (0.7)<10%.

[0131] It was confirmed with this example that in the absence of theheat sink layer 24, a higher setting of the ratio (Pe/Pw) of the erasingpower Pe to the recording power Pw would cause faster degradation injitter and a narrower power margin.

[0132] As described above, defining Jitter (1.0) as the jitter at aratio (Pe/Pw) of the erasing power Pe to the recording power Pw being1.0, the optical recording medium 10 according to this embodimentsatisfies the condition given by

Jitter (1.0)<13%   (1).

[0133] It is therefore possible to reduce jitter in directly overwritingold data with new data even when the ratio of the erasing power to therecording power is increased to thoroughly erase the old data.

[0134] The present invention is not limited to the aforementionedembodiment, and various modifications may also be made thereto withinthe scope of the invention defined in the claims, the modifications alsobeing contained within the scope of the present invention.

[0135] For example, in the aforementioned embodiment, the structureshown in FIG. 2 was cited as a specific structure of the opticalrecording medium 10; however, the structure of the optical recordingmedium according to the present invention is not limited thereto.

[0136] Industrial Applicability

[0137] The present invention is configured as described above, and thuscan provide an advantageous effect of efficiently dissipating heatproduced by a laser beam during recording operations to thereby increasethe erasing power relative to the recording power of the laser beam.

[0138] Accordingly, a very wide power margin provided makes it possibleto record data with stability.

1-13. (Canceled)
 14. An optical recording medium having at least arecording layer, for recording information in the form of recordingmarks being created in the recording layer with a recording laser beam,wherein jitter of recording marks is 13% or less, the recording marksbeing formed at a Pe/Pw setting of 1.0, where Pw is a recording power ofthe recording laser beam and Pe is an erasing power.
 15. The opticalrecording medium according to claim 14, wherein the jitter of recordingmarks is 11% or less, the recording marks being formed at a Pe/Pwsetting of 1.0.
 16. The optical recording medium according to claim 14,wherein the jitter of recording marks is 10% or less, the recordingmarks being formed at a Pe/Pw setting of 0.7.
 4. The optical recordingmedium according to claim 1, wherein the jitter of recording marks is 9%or less, the recording marks being formed at a Pe/Pw setting of 0.7. 17.The optical recording medium according to claim 14, further including alight-transmitting layer provided on a side of incidence of therecording laser beam, and a dielectric layer and a heat sink layerprovided between the recording layer and the light-transmitting layer.18. The optical recording medium according to claim 15, furtherincluding a light-transmitting layer provided on a side of incidence ofthe recording laser beam, and a dielectric layer and a heat sink layerprovided between the recording layer and the light-transmitting layer.19. The optical recording medium according to claim 16, furtherincluding a light-transmitting layer provided on a side of incidence ofthe recording laser beam, and a dielectric layer and a heat sink layerprovided between the recording layer and the light-transmitting layer.20. The optical recording medium according to claim 17, furtherincluding a light-transmitting layer provided on a side of incidence ofthe recording laser beam, and a dielectric layer and a heat sink layerprovided between the recording layer and the light-transmitting layer.21. The optical recording medium according to claim 18, wherein the heatsink layer has a thickness of 10 to 200 nm.
 22. The optical recordingmedium according to claim 19, wherein the heat sink layer has athickness of 10 to 200 nm.
 23. The optical recording medium according toclaim 20, wherein the heat sink layer has a thickness of 10 to 200 nm.24. The optical recording medium according to claim 21, wherein the heatsink layer has a thickness of 10 to 200 nm.
 25. The optical recordingmedium according to claim 18, wherein the heat sink layer has athickness of 30 to 100 nm.
 26. The optical recording medium according toclaim 17, wherein the heat sink layer has a thickness of 30 to 100 nm.27. The optical recording medium according to claim 20, wherein the heatsink layer has a thickness of 30 to 100 nm.
 28. The optical recordingmedium according to claim 21, wherein the heat sink layer has athickness of 30 to 100 nm.
 29. A recording system for an opticalrecording medium, the system including an optical recording mediumprovided with at least a light-transmitting layer covered with arecording layer formed on a support substrate, and a radiation opticalsystem for recording, reproducing, and erasing information on therecording layer by radiating the optical recording medium from thelight-transmitting layer side with a laser beam at a recording power Pwand an erasing power Pe, wherein the radiation optical system isdesigned to radiate the recording layer with a laser beam of wavelength450 nm or less through a lens system having an objective lens ofnumerical aperture 0.7 or more, and the optical recording medium isdesigned to be able to record or erase information on the recordinglayer when the relation between the recording power Pw of the laser beamand the erasing power Pe satisfies 0.7≦Pe/Pw≦1.0.
 30. The recordingsystem for an optical recording medium according to claim 30, whereinthe radiation optical system is designed to radiate the recording layerto record information thereon with a laser beam of wavelength 450 nm orless through a lens system having an objective lens of numericalaperture 0.7 or more, and the optical recording medium is designed toprovide a playback jitter value of 10% or less for the informationrecorded.
 31. The recording system for an optical recording mediumaccording to claim 30, wherein the radiation optical system is designedsuch that the laser beam has a wavelength of 380 nm or more.
 32. Therecording system for an optical recording medium according to claim 31,wherein the radiation optical system is designed such that the laserbeam has a wavelength of 380 nm or more.
 33. The recording system for anoptical recording medium according to claim 30, wherein the radiationoptical system is designed such that the laser beam has a wavelength of405 nm, and the lens system is designed to have an objective lens ofnumerical aperture 0.85.
 34. The recording system for an opticalrecording medium according to claim 31, wherein the radiation opticalsystem is designed such that the laser beam has a wavelength of 405 nm,and the lens system is designed to have an objective lens of numericalaperture 0.85.
 35. The recording system for an optical recording mediumaccording to claim 30, wherein the recording layer is provided, on itslight-transmitting layer side, with a heat sink layer.
 36. The recordingsystem for an optical recording medium according to claim 31, whereinthe recording layer is provided, on its light-transmitting layer side,with a heat sink layer.
 37. The recording system for an opticalrecording medium according to claim 32, wherein the recording layer isprovided, on its light-transmitting layer side, with a heat sink layer.38. The recording system for an optical recording medium according toclaim 33, wherein the recording layer is provided, on itslight-transmitting layer side, with a heat sink layer.
 39. The recordingsystem for an optical recording medium according to claim 36, whereinthe heat sink layer has a thickness of 10 nm or more and 200 nm or less,preferably, has a thickness of 30 nm or more and 100 nm or less.
 40. Therecording system for an optical recording medium according to claim 37,wherein the heat sink layer has a thickness of 10 nm or more and 200 nmor less, preferably, has a thickness of 30 nm or more and 100 nm orless.
 41. The recording system for an optical recording medium accordingto claim 35, wherein the heat sink layer has a thickness of 10 nm ormore and 200 nm or less, preferably, has a thickness of 30 nm or moreand 100 nm or less.
 42. The recording system for an optical recordingmedium according to claim 39, wherein the heat sink layer has athickness of 10 nm or more and 200 nm or less, preferably, has athickness of 30 nm or more and 100 nm or less.